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2551847 
Journal Article 
Letter 
Acid dissociation versus molecular association of perfluoroalkyl oxoacids: Environmental implications 
Cheng, Jie; Psillakis, E; Hoffmann, MR; Colussi, AJ 
2009 
Yes 
Journal of Physical Chemistry A
ISSN: 1520-5215 
113 
29 
8152-8156 
English 
Perfluorooctanoate (PFO) and perfluorooctanesulfonate (PFOS) surfactant anions, once released, may rapidly reach remote regions. This phenomenon is puzzling because the water-bound anions of strong F-alkyl acids should be largely transported by slow oceanic currents. Herein, we investigate whether these hydrophobic F-alkyl oxoanions would behave anomalously under environmental conditions, as suggested elsewhere. Negative electrospray ionization mass spectra of micromolar aqueous PFO or PFOS solutions from pH 1.0 to 6.0 show (1) m/z = 499 (PFOS) signals that are independent of pH and (2) m/z = 413 (PFO) and 369 (PFO - CO(2)) signals, plus m/z = 213 (C(3)F(7)CO(2)(-)) and 169 (C(3)F(7)(-)) signals at higher collision energies, and, below pH similar to 4, m/z = 827 signals from a remarkably stable (PFO)(2)H(-) cluster that increase with decreasing pH. Since the SUM of the m/z = 369, 413, and 827 signal intensities is independent of pH, that is, effectively encompasses all major species, we infer that pK(a)(PFOSA) < 1.0 and pK(a)(PFOA) < 1.0. We also derive K(2) <= 4 x 10(7) M(-2) for the clustering equilibrium 2PFO + H(+) (sic) (PFO)(2)H. Thus, although (PFO)2H is held together by an exceptionally strong homonuclear covalent hydrogen bond, neither PFOS nor PFO will associate or protonate significantly at environmentally relevant subnanomolar concentrations above pH similar to 1. 
• ^Per- and Polyfluoroalkyl Substances (PFAS)
     PFOA (335-67-1) and PFOS (1763-23-1)
          Literature Search – Adverse outcome pathway (2015-present)
               Additional Strategies
     PFBS (375-73-5)
          Literature Search
               Additional Strategies
     PFDS (335-77-3)
          Literature Search
               Additional Strategies
     PFNS (68259-12-1)
          Literature Search
               Additional Strategies
     PFHpS (375-92-8)
          Literature Search
               Additional Strategies
     PFHxS (355-46-4)
          Literature search
               Additional Strategies
     PFPeS (2706-91-4)
          Literature Search
               Additional Strategies
     PFOSA (754-91-6)
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               Pubmed
               WOS
• PFBS
          Additional Strategies
          Chemical/physical properties
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          Other Sources
     Excluded
• PFDS
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          Additional Strategies
• PFHpS
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          Additional Strategies
     Screening Results
          Chemical/physical properties
• PFHxS
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          Additional Strategies
     Screening Results
          Chemical/physical properties
• PFNS
     Literature Search
          Additional Strategies
     Screening Results
          Chemical/physical properties
• PFOA (335-67-1) and PFOS (1763-23-1)
     Literature Search – Adverse outcome pathway (2015-present)
          Additional Strategies
     Screening Results
          Chemical/physical properties
• PFOSA
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          Pubmed
          WOS
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          Excluded/Not on Topic
• PFPeS
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          Additional Strategies
     Screening Results
          Chemical/physical properties